Plate Boundaries (WJEC GCSE Chemistry)

Plate Boundaries

• Earthquakes and volcanoes occur in regions where the edges of different plates are in contact

• So, scientists have been able to identify tectonic plates by gathering and plotting data about:

  • The epicentres of major earthquakes

  • The sites of active volcanoes

World map of earthquakes and volcanoes

The position of earthquakes and volcanoes provides evidence for tectonic plates

Types of plate boundary

• Volcanic eruptions and earthquakes most commonly occur at or near plate boundaries

• There are main types of plate boundaries:

  • Constructive

  • Destructive

  • Conservative

Constructive plate boundary

• At a constructive boundary, tectonic plates are moving apart

  • The Mid-Atlantic Ridge is an example of a constructive plate boundary

• Both volcanic eruptions and earthquakes occur at this type of plate boundary

• The volcanic activity produces new igneous rock

Constructive Plate Boundary

At a constructive plate boundary, the tectonic plates move apart and lava erupts to form the new rock of the tectonic plates

Destructive plate boundary

• At a destructive plate boundary, the plates are moving together

• One tectonic plate is pushed down into the mantle where it melts to form magma

  • The boundary between the Nazca plate and the South American plate is one example

• Both volcanic eruptions and earthquakes occur at this type of plate boundary

• Volcanoes at destructive plate boundaries are explosive 

Destructive Plate Boundary

At a destructive plate boundary, one tectonic plate is pushed under another and melts into the mantle

Conservative boundary

• At a conservative boundary, the plates move past each other in opposite directions or the same direction at different speeds

  • The San Andreas fault is an example of a conservative plate boundary

• Powerful earthquakes are the only hazard at this type of boundary

• There are no volcanoes because melting does not occur

Conservative Plate Boundary Diagram

At a conservative plate boundary, tectonic plates slide past each other